From: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
To: Christian Brauner <brauner@kernel.org>, Shuah Khan <shuah@kernel.org>
Cc: Kees Cook <kees@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Jan Kara <jack@suse.cz>, Oleg Nesterov <oleg@redhat.com>,
Aleksa Sarai <cyphar@cyphar.com>,
Andrei Vagin <avagin@google.com>, Kirill Tkhai <tkhai@ya.ru>,
Alexander Mikhalitsyn <alexander@mihalicyn.com>,
Adrian Reber <areber@redhat.com>,
Pavel Tikhomirov <ptikhomirov@virtuozzo.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-kselftest@vger.kernel.org
Subject: [PATCH v3 1/4] pid_namespace: avoid optimization of accesses to ->child_reaper
Date: Tue, 24 Feb 2026 17:47:52 +0100 [thread overview]
Message-ID: <20260224164852.306583-2-ptikhomirov@virtuozzo.com> (raw)
In-Reply-To: <20260224164852.306583-1-ptikhomirov@virtuozzo.com>
To avoid potential problems related to cpu/compiler optimizations around
->child_reaper, let's use WRITE_ONCE (additional to task_list lock)
everywhere we write it and use READ_ONCE where we read it without
explicit lock. Note: It also pairs with existing READ_ONCE with no lock
in nsfs_fh_to_dentry().
Also let's add ASSERT_EXCLUSIVE_WRITER before write to identify to KCSAN
that we don't expect any concurrent ->child_reaper modifications, and
those must be detected.
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
--
v3: Split from main commit. Add ASSERT_EXCLUSIVE_WRITER.
---
kernel/exit.c | 3 ++-
kernel/fork.c | 5 ++++-
kernel/pid.c | 2 +-
3 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index 8a87021211ae..8e5e523dcc79 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -608,7 +608,8 @@ static struct task_struct *find_child_reaper(struct task_struct *father,
reaper = find_alive_thread(father);
if (reaper) {
- pid_ns->child_reaper = reaper;
+ ASSERT_EXCLUSIVE_WRITER(pid_ns->child_reaper);
+ WRITE_ONCE(pid_ns->child_reaper, reaper);
return reaper;
}
diff --git a/kernel/fork.c b/kernel/fork.c
index e832da9d15a4..9ce2d12ec701 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2423,7 +2423,10 @@ __latent_entropy struct task_struct *copy_process(
init_task_pid(p, PIDTYPE_SID, task_session(current));
if (is_child_reaper(pid)) {
- ns_of_pid(pid)->child_reaper = p;
+ struct pid_namespace *ns = ns_of_pid(pid);
+
+ ASSERT_EXCLUSIVE_WRITER(ns->child_reaper);
+ WRITE_ONCE(ns->child_reaper, p);
p->signal->flags |= SIGNAL_UNKILLABLE;
}
p->signal->shared_pending.signal = delayed.signal;
diff --git a/kernel/pid.c b/kernel/pid.c
index 3b96571d0fe6..76c2744493e2 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -219,7 +219,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *arg_set_tid,
* Also fail if a PID != 1 is requested and
* no PID 1 exists.
*/
- if (tid != 1 && !tmp->child_reaper)
+ if (tid != 1 && !READ_ONCE(tmp->child_reaper))
goto out_abort;
retval = -EPERM;
if (!checkpoint_restore_ns_capable(tmp->user_ns))
--
2.53.0
next prev parent reply other threads:[~2026-02-24 16:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-24 16:47 [PATCH v3 0/4] pid_namespace: make init creation more flexible Pavel Tikhomirov
2026-02-24 16:47 ` Pavel Tikhomirov [this message]
2026-02-24 16:47 ` [PATCH v3 2/4] pid: check init is created first after idr alloc Pavel Tikhomirov
2026-02-24 16:47 ` [PATCH v3 3/4] pid_namespace: allow opening pid_for_children before init was created Pavel Tikhomirov
2026-02-24 16:47 ` [PATCH v3 4/4] selftests: Add tests for creating pidns init via setns Pavel Tikhomirov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260224164852.306583-2-ptikhomirov@virtuozzo.com \
--to=ptikhomirov@virtuozzo.com \
--cc=akpm@linux-foundation.org \
--cc=alexander@mihalicyn.com \
--cc=areber@redhat.com \
--cc=avagin@google.com \
--cc=brauner@kernel.org \
--cc=cyphar@cyphar.com \
--cc=david@kernel.org \
--cc=jack@suse.cz \
--cc=juri.lelli@redhat.com \
--cc=kees@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mingo@redhat.com \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=shuah@kernel.org \
--cc=tkhai@ya.ru \
--cc=vincent.guittot@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox